Nitrification inhibitors and the use of polyacids to treat mineral fertilizers containing a nitrification inhibitor

ABSTRACT

The use of inorganic or organic polyacids for the treatment of inorganic fertilizers, in particular the use of the polyacids as a mixture with at least one nitrification inhibitor for the treatment of inorganic fertilizers; the use of selected pyrazole derivatives as nitrification inhibitor in inorganic fertilizers and also as stabilizers of liquid manure or liquid fertilizer formulations, as well as the corresponding treated inorganic fertilizers per se; and novel pyrazole derivatives which can be used as nitrification inhibitors in inorganic fertilizers and also as stabilizers of liquid manure or liquid fertilizer formulations are described.

The invention relates to the use of inorganic or organic polyacids forthe treatment of inorganic fertilizers.

In particular, the invention relates to the use of polyacids as amixture with at least one nitrification inhibitor for the treatment ofinorganic fertilizers, the use of selected pyrazole derivatives asnitrification inhibitor in inorganic fertilizers, and as stabilizers ofliquid manure or liquid fertilizer formulations, and the correspondingtreated inorganic fertilizers per se. Moreover, the present inventionrelates to pyrazole derivatives which can be used as nitrificationinhibitors in inorganic fertilizers, and as stabilizers of liquid manureor liquid fertilizer formulations.

In order to make available to plants in agriculture the nitrogen neededby them, ammonium compounds are mainly employed as fertilizers.

Ammonium compounds are converted microbially to nitrates in the soil ina relatively short time (nitrification). Nitrates, however, can bewashed out of the soil. The portion washed out is in this case no longeravailable for plant nutrition, so that for this reason rapidnitrification is undesirable. For better utilization of the fertilizer,nitrification inhibitors are therefore added to the fertilizer. A knowngroup of nitrification inhibitors are pyrazole compounds.

A problem in the use of pyrazole compounds as nitrification inhibitorsis their high volatility. During the storage of fertilizer preparationscontaining pyrazole compounds, a continuous loss of active compoundoccurs due to evaporation. The pyrazole compounds must therefore beformulated in a nonvolatile form by means of suitable measures.

To fix the pyrazole compounds, these were converted, for example, intotransition metal complexes such as zinc complexes. This is described,for example, in U.S. Pat. No. 4,522,642. The volatility of the activecompounds can thus be reduced. For environmental protection reasons, thewidespread application of zinc, copper or manganese to the soil is,however, undesirable. Complexes of alkali metals or alkaline earthmetals which are environmentally tolerable, are not adequately stable,however, and hydrolyze in the aqueous environment.

It has furthermore been attempted by neutralization of the pyrazolecompounds with mineral acids, such as phosphoric acid or hydrochloricacid, to decrease their volatility. DE-A-4 128 828 describes the use ofnitrates and phosphates of 3-methylpyrazole for the coating offertilizers. U.S. Pat. No. 3,635,690 also describes the stabilization ofpyrazole derivatives by mineral acids, such as hydrochloric acid,sulfuric acid, nitric acid and phosphoric acid. These acidic salts ofthe pyrazole compounds, however, are increasingly susceptible tohydrolysis and for this reason cannot be employed for all applications.

DE-A4 128 828 further describes the sealing of the coated fertilizerwith wax or oil. In the case of hygroscopic active compound salts,however, this process does not lead to a satisfactory resistance tohydrolysis.

Formulations of pyrazoles with polymeric auxiliaries have furthermorebeen employed. Thus DE 260 486 describes formulations of pyrazoles inurea-formaldehyde condensates. The incorporation of the active compoundsinto the polymer matrix, however, suppresses the mobility of the activecompounds in the soil. In this application form, therefore, the finelydivided formulation and fertilizer must be thoroughly mixed with thesoil to be fertilized. Otherwise the nitrification inhibitor remains onthe surface of the earth with the polymer matrix. The need to mixformulation, fertilizer and soil, however, is laborious.

It is an object of the present invention to provide inorganicfertilizers which contain a nitrification inhibitor whose content doesnot significantly change during storage and application of thefertilizer, and which remains in the ground after application of thefertilizer and can display its action there. Furthermore, newnitrification inhibitors shall be provided.

We have found that this object is achieved by use of inorganic ororganic polyacids for the treatment of inorganic fertilizers. In thiscase, the treated inorganic fertilizer contains a nitrificationinhibitor which is present in the inorganic fertilizer or on itssurface. The nitrification inhibitor can furthermore also be employed asa mixture with the polyacid and then passes into this during thetreatment of the inorganic fertilizer employed according to theinvention, preferably onto the surface thereof.

The use of inorganic or organic polyacids for the treatment of inorganicfertilizers which contain nitrification inhibitors leads to an improvedfixation of the nitrification inhibitors in the inorganic fertilizer.The volatility of the nitrification inhibitor is greatly reduced in thiscase, so that the storage stability of the treated inorganic fertilizerincreases. Loss of nitrification inhibitor during a storage period or onapplication to the soil is avoided.

In addition, the treatment according to the invention and the treatedinorganic fertilizer thus obtained have the advantage of ecologicalacceptability. They contain no toxic substances, such as, for example,zinc, copper or manganese, which in relatively large amounts veryseverely restrict environmental tolerability and can lead to soilcontamination.

The treatment according to the invention can furthermore be carried outin a cost-efficient and ecologically tolerable manner. As a result ofthe treatment according to the invention, the amount of nitrificationinhibitors in the inorganic fertilizer can be reduced because of thedecreased volatility, which leads to decreased costs and to a betterenvironmental tolerability of the fertilizers according to theinvention. The object is furthermore achieved by the use of compounds ofthe general formula ##STR1## where the radical R¹ is a hydrogen atom, ahalogen atom or a C₁₋₄ -alkyl radical, the radical R² is a C₁₋₄ -alkylradical and the radical R³ is H or a radical --CH₂ OH, where if R³ is Hthe salt of the compounds with phosphoric acid can also be employed, asnitrification inhibitors. Preferably the compound used is 3,4-dimethylpyrazole, 4-chloro-3-methylpyrazole or a phosphoric acid addition soltthereof.

Polyacids

According to the invention, inorganic or organic polyacids are used forthe treatment of the inorganic fertilizers.

In this case, all suitable inorganic or organic polyacids can be usedwhich decrease the tendency of nitrification inhibitors to evaporate.

Inorganic polyacids which can be used according to the invention areisopolyacids or heteropolyacids, in particular polyphosphoric acids orpolycyclic acids. The polyphosphoric acids, for example, have thegeneral formula H_(n+2) P_(n) O_(3n+1), n being an integer of at least2, preferably at least 10.

Further inorganic polyacids which can be used are known to the personskilled in the art.

Suitable organic polyacids are those polymers which have a plurality offree carboxylic acid groups. These can be homo- or copolymers. Suitablemonomers containing carboxyl groups or carboxylic acid groups are, inparticular, monoethylenically unsaturated mono- or dicarboxylic acidshaving from 3 to 6 C atoms or their corresponding anhydrides, such as,for example, acrylic acid, methacrylic acid, ethylacrylic acid,allylacetic acid, crotonic acid, vinylacetic acid, maleic acid, itaconicacid, mesaconic acid, fumaric acid, citraconic acid, methylenemalonicacid, as well as their esters, such as, for example, monoalkyl maleates,and mixtures thereof. In the case of monoalkyl dicarboxylates, thenumber of C atoms specified relates to the dicarboxylic acid structure,the alkyl group in the ester radical, independently thereof, can havefrom 1 to 20 C atoms, in particular from 1 to 8 C atoms. Suitableappropriate monoethylenically unsaturated dicarboxylic anhydrides aremaleic anhydride, itaconic anhydride, citraconic anhydride and mixturesthereof. Acrylic acid, methacrylic acid, maleic acid, itaconic acid andmaleic anhydride are preferably employed. Acrylic acid is particularlypreferably employed.

These monomers containing carboxyl groups or containing carboxylic acidgroups can be homopolymerized or copolymerized with further vinylicmonomers, such as, for example, C₁₋₈ -, preferably C₁₋₄ -alkylenes, inparticular ethylene or propylene.

The organic polyacid particularly preferably used is polyacrylic acid orpolymethacrylic acid.

The inorganic or organic polyacids can be employed as free acids or aspartially neutralized ammonium, alkali metal or alkaline earth metalsalts thereof. They are preferably employed as free acids.

Polyphosphoric acid and poly(meth)acrylic acid are particularlypreferred.

The mean molecular weight of the organic polyacids is preferably from10,000 to 500,000, particularly preferably from 10,000 to 100,000, inparticular from 30,000 to 70,000.

Processes for the preparation of the polyacids are known to the personskilled in the art.

Nitrification Inhibitors

Any desired suitable nitrification inhibitors can be employed in theinorganic fertilizers according to the invention.

The polyacids used according to the invention are particularlyadvantageously employed for the treatment of inorganic fertilizers whichcontain these volatile nitrification inhibitors, in particular pyrazolecompounds. "Pyrazole compounds" is understood as meaning all pyrazolecompounds which have a nitrification-inhibiting action, such as are alsodescribed, for example, in the publications U.S. Pat. Nos. 3,635,690,4,522,642 and DE-A-4 128 8-28 mentioned at the beginning in thediscussion of the prior art, whose contents with respect to the pyrazolecompounds described there are hereby included.

According to one embodiment, the pyrazole compounds used asnitrification inhibitors are those of the general formula below ##STR2##where the radicals R¹, R² and R³ independently of one another arehalogen atoms, nitro groups, hydrogen atoms or C₁₋₂₀ -, preferably C₁₋₄-alkyl radicals, C₃₋₈ -cycloalkyl radicals, C₅₋₂₀ -aryl radicals oralkylaryl radicals, where the last-mentioned 4 radicals can bemonosubstituted or trisubstituted by halogen atoms and/or hydroxylgroups.

The radical R¹ is preferably a hydrogen atom, a halogen atom or a C₁ -C₄-alkyl radical, the radical R² is a C₁₋₄ -alkyl radical and the radicalR³ is a hydrogen atom or a radical --CH₂ OH.

According to a further embodiment of the invention, the radical R¹ inthe above formula is a halogen atom or C₁₋₄ -alkyl radical, the radicalR² is a C₁₋₄ -alkyl radical and the radical R³ is a hydrogen atom or aradical --CH₂ CH₂ COOH or --CH₂ CH(CH₃)COOH.

The pyrazole compounds can be employed in the basic form, and also inthe form of acid addition salts with inorganic mineral acids and organicacids. Examples of inorganic mineral acids are hydrochloric acid,phosphoric acid, sulfuric acid, preferably phosphoric acid. Examples oforganic acids are formic acid, acetic acid, and also fatty acids.Examples of these salts are the hydrochlorides and phosphoric acidaddition salts.

The pyrazole compounds can be employed on their own or in the form ofmixtures.

Particularly preferred pyrazole compounds are 3,4-dimethylpyrazole,4-chloro-3-methylpyrazole, N-hydroxymethyl-3,4-dimethylpyrazole,N-hydroxymethyl-4-chloro-3-methylpyrazole as well as the phosphoric acidaddition salts of 3,4-dimethylpyrazole and 4-chloro-3-methylpyrazole aswell as the hydrochloride of 3,4-dimethyl-pyrazole.

By use of the acid addition salts of the pyrazole compounds, thevolatility of the compounds can be further reduced. Thus acid additionsalts of the pyrazole compounds are advantageously employed incombination with the treatment according to the invention.

Halogen atoms employed in the above compounds are fluorine, chlorine,bromine or iodine, preferably fluorine, chlorine or bromine.

The preparation of the pyrazole compounds used according to theinvention is known. It is described, for example, in EP-A-0 474 037,DE-A 3 840 342 and EP-A-0 467 707. For preparation of theN-hydroxymethylpyrazoles, the corresponding pyrazoles are reacted withformalin solution in methanol. Excess solvent is then evaporated, thecompounds being obtained as solids. For the preparation of3,4-dimethyl-pyrazole reference is made to Noyce et al., Jour. of Org.Chem. 20, 1955, 1681 to 1682.

The acid addition salts of the pyrazole compounds are obtained byreaction of the pyrazoles with an equivalent of appropriate acid. Thepreparation of the hydrochloride of 4-chloro-3-methyl-pyrazol isdescribed in Huttel et al., Liebigs Ann. Chem. 1956, 598, 186, 194.

Treated Inorganic Fertilizers

According to the invention, inorganic fertilizers are employed. Theseare ammonium- or urea-containing fertilizers. Examples ofammonium-containing fertilizers of this type are NPK fertilizers,calcium ammonium nitrate, ammonium sulfate nitrate, ammonium sulfate orammonium phosphate.

The treated inorganic fertilizer according to the invention can bepresent in powder form or in granule form.

The inorganic fertilizers treated according to the invention contains atleast one nitrification inhibitor and is treated with at least oneinorganic or organic polyacid. In this case, the inorganic fertilizercan be present as a mixture with the nitrification inhibitor. Thenitrification inhibitor can also be present on the surface of theinorganic fertilizer and can then be treated with the polyacid accordingto the invention. Preferably, the nitrification inhibitor can be appliedto the inorganic fertilizer as a mixture with the polyacid to be usedaccording to the invention.

Preferably, the inorganic fertilizer contains as nitrification inhibitora pyrazole compound or an acid salt thereof. Preferably, the inorganicfertilizer is treated with poly(meth)acrylic acid or polyphosphoricacid.

Preferably, the inorganic fertilizer contains from 0.01 to 1.5% byweight of nitrification inhibitor and from 0.01 to 1.5% by weight ofpolyacid, based on the treated inorganic fertilizer.

The present invention furthermore relates to inorganic fertilizerscomprising a compound of the above general formula, as is defined above,and a treated inorganic fertilizer comprising the abovementionedinorganic fertilizer, which is treated with at least one inorganic ororganic polyacid or a mixture of at least one nitrification inhibitorand at least one inorganic or organic polyacid.

Preparation of the Treated Inorganic Fertilizers

The treated inorganic fertilizers according to the invention areprepared by treating the inorganic fertilizer with the polyacid.Preferably, they are prepared by treating the surface of the inorganicfertilizer with the polyacid.

In this case, the nitrification inhibitor can be present as a mixturewith the inorganic fertilizer or can have been applied to the inorganicfertilizer before the polyacid. According to one embodiment of theinvention, the inorganic fertilizer is treated with polyacid andnitrification inhibitor as a mixture.

In this case, the inorganic fertilizers are treated, e.g. impregnated orsprayed, with the polyacid, the nitrification inhibitor or mixturethereof by spraying them with a liquid preparation, e.g. a solution orsuspension of the polyacid, of the nitrification inhibitor or of themixture and, if desired, drying again. An appropriate process isdescribed, for example in DE-A-4 128 828.

Preferably, nitrification inhibitor and polyacid are applied, e.g.sprayed, onto the inorganic fertilizer in the form of a liquidpreparation, e.g. of a solution or suspension of the polyacid, and, ifdesired, then dried.

In this case, a mixture is preferably employed of from 30 to 98% byweight of at least one polyacid and from 2 to 70% by weight of at leastone nitrification inhibitor in a liquid medium, preferably water. Thenitrification inhibitor can in this case again be present as an acidaddition salt.

The invention also relates to the use of compounds of the generalformula ##STR3## where the radical R¹ is a hydrogen atom, a halogen atomor a C₁₋₄ -alkyl radical,

the radical R² is a C₁₋₄ -alkyl radical and

the radical R³ is H or a radical --CH₂ OH, where if R³ is H, the salt ofthe compounds with phosphoric acid can also be employed, asnitrification inhibitors.

Halogen atoms employed in the above compounds are fluorine, chlorine,bromine or iodine, preferably fluorine, chlorine or bromine.

Particularly preferred pyrazole compounds are 3,4-dimethylpyrazole,4-chloro-3-methylpyrazole, N-hydroxymethyl-3,4-dirnethylpyrazole,N-hydroxymethyl-4-chloro-3-methylpyrazole, as well as the phosphoricacid addition salts of 3,4-dimethylpyrazole and4-chloro-3-methylpyrazole. N-Hydroxymethyl-3,4-dimethylpyrazole andN-hydroxymethyl-3,4-chloro-3-methylpyrazole are particularly preferred.

The present invention furthermore relates to a fertilization process, inwhich treated inorganic fertilizer, as defined in the context of thepresent application, is applied to the arable soil.

According to one embodiment of the present invention the nitrificationinhibitors or inorganic fertilizers as described above are not used fortreating soils which are used for corn, cotton, wheat, rice, barleyand/or sugar-beet cultures or for treating the respective cultures.

The compounds of the above general formula can furthermore be used forthe stabilization of liquid manure or liquid fertilizer formulations,such as, for example, ammonium nitrate-urea solutions or liquid ammonia.

The invention furthermore relates toN-hydroxymethyl-4-chloro-3-methylpyrazole, as well as the phosphoricacid addition salts of 3,4-dimethylpyrazole and4-chloro-3-methylpyrazole per se, the hydrochloride of3,4-dimethylpyrazole as well as mixtures of two or more thereof, which,of course, can also be used as nitrification inhibitors, preferablytogether with the polyacids used according to the invention.

The invention is further described below by means of examples.

EXAMPLES Preparation of N-hydroxymethyl-3,4-dimethylpyrazole

96 g (1.0 mol) of 3,4-dimethylpyrazole in 50 ml of methanol weredissolved in 100 g (1.0 mol) of formalin solution (30%) at roomtemperature. Water and methanol were then evaporated. The title compoundremained as a white solid (yield 95%).

Preparation of N-hydroxymethyl-4-chloro-3-methylpyrazole

116 g (1.0 mol) of 4-chloro-3-methylpyrazole in 50 ml of methanol weredissolved in 100 g (1.0 mol) of formalin solution (30%) at roomtemperature. Water and methanol were then evaporated. The title compoundremained as a white solid (yield 95%).

Preparation of 3,4-dimethylpyrazolium dihydrogen phosphate

96 g (1.0 mol) of 3,4-dimethylpyrazole were dissolved in 115 g (1.0 mol)of phosphoric acid (85%) at room temperature. The water contained in thephosphoric acid was evaporated. After a few hours, the title compoundcrystallized out from the oil initially present (yield 98%).

Preparation of 4chloro-3-methylpyrazolium dihydrogen phosphate

116 g (1.0 mol) of 4-chloro-3-methylpyrazole were dissolved in 115 g(1.0 mol) of phosphoric acid (85%) at room temperature. The watercontained in the phosphoric acid was evaporated. After a few hours, thetitle compound crystallized out of the oil initially present (yield98%).

Preparation of the Nitrification-inhibited Inorganic Fertilizers

The carrier fertilizer used was ammonium sulfate nitrate (ASN). 2 g ofpyrazole were dissolved in a little water, and if desired (see Table I)the solution was mixed with a stoichiometric amount of phosphoric acid(1:1) and with from 1 to 10 g of polyacrylic acid or polyphosphoricacid. 2 g of the carrier fertilizer in the form of granules wereprewarmed to approximately 50° C. and slowly sprayed onto a turntablewith the mixture containing the pyrazole compound. To accelerate thedrying, drying was carried out with hot air, either at the end of thespraying or after interruption of the spraying.

Investigation of the Storage Stability

The storage stability of the treated inorganic fertilizers wasdetermined in a rapid test in which the nitrification-inhibitedinorganic fertilizers were stored in a ventilated warming cabinet for 4weeks at 30° C., from 40 to 50% relative atmospheric humidity andapproximately 1.2 m/s air velocity. The concentration of nitrificationinhibitor on the inorganic fertilizer was determined before and afterstorage and the loss of nitrification inhibitor determined in percent.Approximately 10 to 30 g of treated inorganic fertilizer were stored ineach case. The concentration of pyrazole compound as nitrificationinhibitor in this case was from 0.05% by weight to 0.2% by weight at thestart of the investigation, based on the treated inorganic fertilizer.The losses obtained for different pyrazole compounds are shown in TableI below.

                  TABLE I                                                         ______________________________________                                        Compound                Loss in percent                                       ______________________________________                                        3-Methylpyrazole*       100%                                                  3,4-Dimethylpyrazole*   100%                                                  4-Chloro-3-methylpyrazole*                                                                            100%                                                  3-Methylpyrazole phosphate*                                                                           55%                                                   3,4-Dimethylpyrazole phosphate*                                                                       31%                                                   4-Chloro-3-methylpyrazole phosphate*                                                                  92%                                                   3,4-Dimethylpyrazole + polyacrylic acid                                                               10%                                                   4-Chloro-3-methylpyrazole + polyacrylic acid                                                          5%                                                    3,4-Dimethylpyrazole phosphate + polyacrylic                                                          9%                                                    acid                                                                          4-Chloro-3-methylpyrazole phosphate +                                                                 12%                                                   polyacrylic acid                                                              3,4-Dimethylpyrazole + polyphosphoric acid                                                            0%                                                    (1:20)                                                                        3,4-Dimethylpyrazole + polyphosphoric acid                                                            12%                                                   (1:1)                                                                         ______________________________________                                         *= Comparison experiments                                                

It emerges from the results of Table I that the loss of pyrazolecompound in the inorganic fertilizers treated according to the inventionduring storage is essentially lower than with the comparison substances.Coating with the polyacid according to the invention leads to asignificantly reduced loss of nitrification inhibitor.

Demonstration of the Biological Effect of the Nitrification Inhibitors

Field Test

The biological effectiveness of 4-chloro-3-methylpyrazole (4 Cl-3MP) and3,4-dimethylpyrazole (3,4-DMP) in comparison with DCD and the controlwas tested in multiple field tests in different environments by means ofthe features "nitrate content in the basis of the stem", "NO₃ -- and NH₄--N-content in the soil" as well as "grain produce".

The standard methods used in agricultural tests were applied to thelaying-out, probing, harvesting and evaluation of the field tests.

The analysis of the plant and soil samples followed standard procedures.The remaining measures undertaken in the production, e.g. plantprotection, were in accordance with good agricultural practice and wereapplied uniformly.

A biologically effective nitrification inhibitor is characterizedpreferably in that the soil to which it is applied shows lower amountsof NO₃ --N and higher amountes of NH₄ --N compared to a comparitive test(here: supporting fertilizer is ammonium sulfate salpeter withoutnitrification inhibitor) in a time period of up to 8 weeks afterapplication (compare table 1).

As a consequence of this treatment the nitrate consumption of the plantsis reduced (compare NO₃ -content in the basis of the stem of rapeplants, table 2) and the produce is enhanced (compare grain produce ofwinter wheat, tables 3a and 3b). Table 4 shows the description of thelocation of the field tests.

In the following table 1 the results are summarized. It is evident thatall three nitrification inhibitors have good biological effectivenesscompared to the control. 4 Cl-3 MP and 3,4-DMP show an effectiveness asgood as or better than that of DCD, using reduced amounts of the activesubstance. Further examples relating to selected nitrificationinhibitors are shown in table 5.

                                      TABLE 1                                     __________________________________________________________________________    Demonstration of the biological effect of different nitrificaion              inhibitors                                                                    field tests                                                                   φ NO3- and NH4-N-amounts in soil (n = 5)                                         weeks after application                                                       2       4       6       8                                              nitrification                                                                        NO3-N                                                                             NH4-N                                                                             NO3-N                                                                             NH4-N                                                                             NO3-N                                                                             NH4-N                                                                             NO3-N                                                                             NH4-N                                      inhibitor                                                                            kg/ha                                                                             kg/ha                                                                             kg/ha                                                                             kg/ha                                                                             kg/ha                                                                             kg/ha                                                                             kg/ha                                                                             kg/ha                                      __________________________________________________________________________    without                                                                              82  97  75  49  61  50  43  20                                         DCD    47  87  44  68  35  82  29  39                                         4Cl-3MP                                                                              61  115 50  79  39  76  28  40                                         3,4-DMP                                                                              54  82  43  70  44  71  28  37                                         __________________________________________________________________________     locations: 1,2,3,4 and 5: description see table 4                        

                  TABLE 2                                                         ______________________________________                                        demonstration of the biological effect of different nitrification             inhibitors                                                                    field tests -                                                                 .O slashed. NO3 amount in the basis of the stem of rape plants (n = 5)                  weeks after application                                                       2    4          6      8                                            ______________________________________                                        nitrification                                                                             NO3    NO3        NO3  NO3                                        inhibitor   ppm    ppm        ppm  ppm                                        without     8421   7255       5642 5194                                       DCD         8036   7022       4728 4274                                       4Cl-3MP     8112   6629       4774 4276                                       3,4-DMP     8105   6720       4899 4454                                       ______________________________________                                         locations: 1,2,3,4 and 5: description see table 4                        

                  TABLE 3a                                                        ______________________________________                                        demonstration of the biological effect of different nitrification             inhibitors                                                                    field tests -                                                                 grain produce of winter wheat                                                 nitrification grain produce                                                   inhibitor     dt/ha                                                           ______________________________________                                        without       52,8                                                            DCD           52,6                                                            4Cl-3MP       56,0                                                            ______________________________________                                         location 4: description see table 4                                      

                  TABLE 3b                                                        ______________________________________                                        demonstration of the biological effect of different nitrification             inhibitors                                                                    field tests -                                                                 grain produce of winter wheat                                                 nitrification grain produce                                                   inhibitor     dt/ha                                                           ______________________________________                                        without       95,4                                                            DCD           94,3                                                            3,4-DMP       97,8                                                            ______________________________________                                         location 2: description see table 4                                      

                  TABLE 4                                                         ______________________________________                                        demonstration of the biological effect of different nitrification             inhibitors                                                                    field tests -                                                                 description of the location                                                         temper- precip-                                                               ature   itation       arable        humus                                     per year                                                                              per year                                                                              type  soil          content                             location                                                                            ° C.                                                                           mm      of soil*                                                                            number                                                                              pH-value                                                                              %                                   ______________________________________                                        1     8,8     600     L     68    7,3     1,3                                 2     7,8     817     tL    43    6,6     1,4                                 3     10,1    740     sL    45    6,5     1,2                                 4     9,9     550     IS    30    6,5     1,2                                 5     9,9     550     L     60    6,7     1,3                                 ______________________________________                                         *L: loam                                                                      tL: lean clay                                                                 sL: sandy loam                                                                IS: loamy sand                                                           

                  TABLE 5                                                         ______________________________________                                        nitrification inhibiting effect of different pyrazoles*                       compound        1        2     4     6   8                                    ______________________________________                                        3-methylpyrazole (3-MP)                                                                       90       58    45    27  22                                   3,4-dimethylpyrazole (DMP)                                                                    88       61    48    34  27                                   4Cl-3methylpyrazole (4Cl-3MP)                                                                 88       66    48    32  21                                   4Cl-3methylpyrazolephosphate                                                                  91       62    53    45  27                                   N-hydroxy-4Cl-3MP                                                                             87       58    45    30  15                                   N-hydroxyl-3,4-DMP                                                                            85       54    40    31  10                                   ______________________________________                                         *% inhibition per applied amount of ammonium                             

We claim:
 1. A pyrazole derivative selected from the group consistingofN-hydroxymethyl-4-chloro-3-methylpyrazole,N-hydroxymethyl-3,4-dimethyl pyrazole, phosphoric acid addition salt of3,4-dimethylpyrazole, phosphoric acid addition salt of4-chloro-3-methylpyrazole, and hydrochloride of 3,4-dimethylpyrazole. 2.A method of using a pyrazole derivative as defined in claim 1 as anitrification inhibitor.
 3. An inorganic fertilizer comprising at leastone pyrazole derivative as defined in claim
 1. 4. An inorganicfertilizer as defined in claim 3 in powder form or in granule form,treated with at least one inorganic or organic polyacid.
 5. An inorganicfertilizer as defined in claim 4, where the inorganic or organicpolyacid is present in an amount from 0.01 to 1.5% by weight, and thepyrazole derivative is present as nitrification inhibitor in an amountfrom 0.01 to 1.5% by weight, based on the treated inorganic fertilizer.6. A pyrazole derivative as defined in claim 1, which isN-hydroxymethyl-4-chloro-3-methylpyrazole.
 7. A pyrazole derivative asdefined in claim 1, which is N-hydroxymethyl-3,4-dimethylpyrazole.
 8. Apyrazole derivative as defined in claim 1, which is phosphoric acidaddition salt of 3,4-dimethylpyrazole.
 9. A pyrazole derivative asdefined in claim 1, which is phosphoric acid addition salt of4-chloro-3-methylpyrazole.
 10. A pyrazole derivative as defined in claim1, which is hydrochloride of 3,4-dimethylpyrazole.
 11. A mixture of twoor more pyrazole derivatives as defined in claim 1.